SERVER-67775 Add TicketAcquisitionPriority to the Locker class

1 files changed, 31 insertions, 0 deletions

diff --git a/src/mongo/util/concurrency/ticketholder.h b/src/mongo/util/concurrency/ticketholder.h
index cc571041344..1882d2168b1 100644
--- a/src/mongo/util/concurrency/ticketholder.h
+++ b/src/mongo/util/concurrency/ticketholder.h
@@ -49,6 +49,12 @@ namespace mongo {
 class Ticket;
 class ReaderWriterTicketHolder;
 
+/**
+ * A ticket mechanism is required for global lock acquisition to reduce contention on storage
+ * engine resources.
+ *
+ * Manages the distribution of tickets across operations.
+ */
 class TicketHolder {
     friend class Ticket;
 
@@ -56,6 +62,31 @@ public:
     virtual ~TicketHolder(){};
 
     /**
+     * Classifies the priority that an operation acquires a ticket when the system is under high
+     * load (operations are throttled waiting for a ticket). Only applicable when there are no
+     * available tickets.
+     *
+     * 'kLow': It's of low importance that the operation acquires a ticket. These low-priority
+     * operations are reserved for background tasks that have no other operations dependent on them.
+     * These operations may be throttled under load and make significantly less progress as compared
+     * to operations of a higher priority.
+     *
+     * 'kNormal': It's important that the operation be throttled under load. If this operation is
+     * throttled, it will not affect system availability or observability. Most operations, both
+     * user and internal, should use this priority unless they qualify as 'kLow' or 'kHigh'
+     * priority.
+     *
+     * 'kHigh': It's crucial that the operation makes forward progress - bypassing ticket
+     * acquisition. Reserved for operations critical to availability (e.g. replication workers) or
+     * observability (e.g. FTDC), and any operation that is releasing resources (e.g. committing or
+     * aborting prepared transactions). Should be used sparingly.
+     *
+     * TODO SERVER-67951: Update comment to address that kHigh priority operations are always
+     * granted a ticket immediately upon request.
+     */
+    enum class AcquisitionPriority { kLow, kNormal, kHigh };
+
+    /**
      * Wait mode for ticket acquisition: interruptible or uninterruptible.
      */
     enum WaitMode { kInterruptible, kUninterruptible };